This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. 'Background. Neurobiology of psychopathy remains obscure. Medial temporal lobe pathology has been suggested to be a part of the neural systems dysfunction which manifests as violent and psychopathic behavior. In a previous study, Laakso and colleagues measured regional hippocampal volumes using magnetic resonance and found that the regional volumes along the anteroposterior axis of the hippocampus were correlated with the subjects'degree of psychopathy. Strong negative correlations were observed between the psychopathy scores and the posterior half of the hippocampi bilaterally. Aim. To locate in vivo the structural changes within the hippocampal formation in subjects with psychopathy. Methods. Twenty-six men with psychopathy (age:32[unreadable]8) and 25 controls (35[unreadable]11) were included in this study. Psychoapthy were assessed using the Psychopathy Checklist-Revised. The hippocampal formation will be isolated by manually tracing on 35 coronal slices the outlines of the hippocampus proper and subiculum after registration to a common stereotactic space. Group differences will be assessed with algorithms developed ad hoc that make use of three-dimensional parametric surface mesh models. Expected results. We expect that regional differences within the hippocampal formation should exist between psychopathy and controls and should be in line with previous results obtained with volumetric measurements (Laakso et al, 2001).